The surface properties of an implant are crucial to the bioacceptability and the biocompatibility of the implant. Firstly, the texture or morphology of the surface is crucial for the growth of new cells on the implant. Secondly, the growth of desired cells can be encouraged by releasing active substances, or the growth of undesirable cell clusters, such as introduced bacteria, which may lead to an infection or even cause the implant to be rejected, can be inhibited.
For these reasons, coatings which are produced in sol-gel processes and release active substances have been developed in the prior art. This release of active substances may have an antibacterial effect for example, as disclosed in DE 10243132. However, the use thereof is limited to metal ions, the organic salts of which can be dissolved in a sol.
In an attempt to adapt the texture of an implant to natural conditions, WO 2004/103421 A1 discloses a bone substitute material in the form of a granular material which is formed using a calcium phosphate powder in a sol-gel process. This granular material can be coated onto an implant but must, however, be applied by an expensive method, a plasma spraying method for example.
A similar material is disclosed in application DE 10 2004 012411 A1 by DOT Coating. Application as a layered system with a defined surface texture is not described. It is also not possible to texture the surface in a targeted manner. In addition, the material contains a polysilicic acid-based composite material which contains an organic polymer. However, this material has the drawback that it has a reduced stability in storage on account of the organic components and is difficult to sterilise with the γ-radiation sterilisation method which is conventional in the medical field. A subsequent sterilisation procedure in hospital is also hindered by the fact that heating the material to 132° C. results in degradation of the organic components. Furthermore, an active substance, such as an antibiotic or a polymer, present in the material can be damaged or immobilised by radicals produced by γ-radiation.
DE 102 43 132 B4 discloses an antimicrobial titanium oxide coating for implants which is prepared in a sol-gel process. In this application, the metal salt used is homogeneously and completely dissolved in the sol-gel matrix and is not present as solid particles, and it is therefore not possible to texture the surface.
DE 600 22 197 T2 discloses a material, for example, in the form of particles which are prepared in a sol-gel process. Adding particles while carrying out the sol-gel process is not mentioned. In addition, the material must be heated to temperatures of 800 to 1,500° C. for hardening purposes.
A simple sol-gel coating without a powder filler is known from the publication by M. Jokinen et al., J. Biomed. Mater. Res., 42 (1998) 295-302.
Finally, a porous material which can be charged with antibiotics to produce an antimicrobial element is known from M. Teller et al., Key Engineering Materials, Vols. 284-286 (2005), pages 415-418. This material is not suitable for coating an implant due to the high porosity of the material.
All the aforementioned processes have the drawback that it is not possible to texture the surface in a purposeful manner and to adjust the release of the active substance.
The object of the present invention is therefore to provide a process for preparing a coating which enables the surface texture morphology of a coating on a substrate to be adjusted in a purposeful manner, it also being possible to adjust the release of an active substance.